Exposure to oxidative stress conditions and the generation of excessive reactive oxygen species (ROS) are generally hypothesized to be a common causative factor in the etiology of several human diseases including, but not limited to, fatty liver disease, dyslipidemia, insulin-resistant type 2 diabetes, cardiovascular disease/hypertension, and obesity (collectively known as Metabolic Syndrome). Although it is well established that lipids, proteins and nucleic acids are critical cellular targets for endogenously and exogenously produced ROS, until recently, deficiencies in repair of ROS-induced DNA base damage had not been considered to be key in the aforementioned diseases, while being considered central to carcinogenesis. However, two knockout mouse models (neil1 and ogg1) have been created in which the initiation of base excision repair of oxidatively-damaged DNA is defective, and in both models, mice develop subsets of symptoms consistent with Metabolic Syndrome. Disease manifestations in the neil1 knockout mice may include obesity, fatty liver disease, dyslipidemia and hyperinsulinemia, with male knockouts much more severely affected than females. In addition, analyses of nuclear DNAs isolated from these mice reveal the accumulation of high levels of ROS-damaged bases and mitochondrial DNAs (mtDNA) show both increased steady-state base damage and large deletions relative to control littermates. Since it known that excessive oxidative stress can induce symptoms of Metabolic Syndrome in repair-proficient organisms, it is hypothesized that the loss of NEIL1 or OGG1 lowers the threshold at which oxidatively stress-induced disease is manifested. In the absence of repair, the progressive accumulation of compromised mtDNA genomes leads to deficiencies in energy production, as well as alterations in free fatty acid and lipid metabolism. In order to test this hypothesis, multiple physiological parameters will be evaluated for changes in neil1-/-, ogg1-/- and neil1-/-ogg1-/- mice and their wild-type littermates during pro-oxidant challenges versus control conditions. These data will be correlated with rates of pathological changes and mitochondrial and nuclear DNA damage accumulation as measured by GC/MS and quantitative PCR. These analyses will be complemented by examining the role of NEIL1 in the modulation of survival, mutagenesis, and mitochondrial function in response to oxidative or nitric oxide stress conditions. Further, since repair of mtDNA is hypothesized to be critical in maintaining metabolic homeostasis, experimental designs are proposed to establish intracellular distribution of various NEIL1 isoforms and determine the biological consequences of expressing nuclear or mitochondrially-targeted forms of these enzymes in neil1-/- cells.

Public Health Relevance

The growing epidemic of human obesity is currently estimated to affect over 60 million adult Americans, with secondary consequences including, but not limited to, fatty liver disease, cardiovascular disease, and insulin resistance/type 2 diabetes, collectively known as the Metabolic Syndrome. A potential underlying molecular mechanism for these diseases is suggested by the study of DNA repair-deficient mouse models that lack oxidative DNA base damage repair and exhibit many of the defining hallmarks of the Metabolic Syndrome: severe obesity, fatty liver disease, dyslipidemia, and insulin resistance. These investigations will examine the role of reduced DNA repair in the onset and progression of these diseases.